"What a story," says Philip Sutcliffe, a two-time Olympian who has run this gym through testing times.

"A kid, a plumber, unemployed, then cage fighting. What a story."

The bank job

Conor McGregor has previously tweeted this mocked-up picture of the two fighters

There are many who do not give McGregor even a puncher's chance. Crumlin Boxing Club built the fundamentals of a left hand which has wiped out stellar names such as Jose Aldo and Eddie Alvarez and led to world titles in two UFC weight divisions, yet in the eyes of almost the entire boxing fraternity, that schooling will prove nowhere near enough.

Dubbed "a farce" or "a hoax" by some and "an event" by the more kind, try telling the children gloved up in the Crumlin ring or those who filter through this community club that Mayweather-McGregor is anything other than a boxing match.

"When it was announced we couldn't help but laugh," admits BBC boxing correspondent Mike Costello. "It just had the feeling of two men who have pulled off a bank job, everyone knows they have but they can't be bothered to arrest them because it's going to be such a good crack."

But time spent in the warm company of Sutcliffe is intoxicating. He has seen a 12-year-old McGregor walk into the gym from an adjacent football field and become the multi-millionaire poster boy of UFC. Why wouldn't he believe the underdog can prevail?

"Conor is different because he doesn't think like a boxer," says Sutcliffe, who went to the 1980 and 1984 Olympic Games for Ireland. "Conor thinks like an octagon fighter. They move back to land a punch so they don't get caught in a grapple. Conor is a master of that.

"Mayweather likes to fight beautiful fighters but when someone is different, is he able to handle it? Conor is that, he's special. Special in the way he throws punches, the way he carries himself. Why can't he clip him? Just one second, that's all it takes and he'd change the rhythm of the fight."

The early McGregor

McGregor's MMA record stands at 21 wins and three losses

YouTube is awash with videos of a younger, more timid McGregor stating, with hope rather than certainty, that he would leave his mark in UFC.

Those dreams were born at the Crumlin base, where punch bags of all shapes and sizes hang from the ceiling, trophies line window ledges and fight posters offer a raw wallpaper.

It was enough to hook McGregor but his thirst for combat saw him taken by other disciplines so much that his exposure to pure boxing competitions was limited.

"Hands up, elbows in, chin down, we teach them that straight away," says Sutcliffe. "He was one of the diligent ones and he tried hard. You only had to show him once.

"We try to build them towards the Olympics and Conor could have been one of them, but he was into a few things like Jiu-Jitsu and grappling. He didn't go into the competitions because he was elsewhere practising something else.

"Whatever he did, he put 100% in. He sparred hard against some of the best in the club. You see how good he is in the octagon, you can see how he moves his feet, he learned that here."

Nerveless confidence will unease Mayweather

McGregor's path to the top of UFC was not without road bumps. Shortly after his first pro MMA win aged 18, a lost focus saw his mother phone his current coach John Kavanagh with a plea for him to tempt her son back into the gym.

McGregor himself says her desire was because he was visibly "happier" in life after workouts and her move was inspired. Less than 10 years later he made the Forbes Top-100 list of the world's best paid athletes, bringing in around £27m in 2017.

Success has delivered confidence and brought out a personality which will form part of a product marketable in a way no other Las Vegas bout has ever been.

And yet he has no wins and no losses. A statement which in the context, looks as off as it reads.

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Mayweather v McGregor: The kings of trash talk

But despite seeking a fight with a man unbeaten in 49 bouts, McGregor demanded respect when talking up this fight. He has been consistently emphatic. "No one in this boxing game knows what's coming," he told reporters in March. "Trust me I'm going to shock the whole God damn world."

BBC Radio 5 live boxing pundit Steve Bunce says: "If McGregor keeps up that confidence, Mayweather will not like it. He is not used to seeing confidence in front of him, and he hates people being more loved than him."

But this is Mayweather's sport in the Las Vegas city which falls over itself to please the five-weight world champion. 'Money' will do all he can to make McGregor feel like an underdog. Fight week will likely offer never before seen hype, with Mayweather controlled, pulling strings to gain an edge in the shadows.

"Conor never carried nerves," adds Sutcliffe. "He wanted to fight. He was cute, didn't get hit and so he just didn't show nerves."

Then, running his hands veil like down Costello's face, Sutcliffe adds: "Show no emotion, that is the Crumlin way."

'It simply cannot happen'

Mayweather has won boxing world titles at five weights

Sutcliffe points out: "Mayweather is a master of making people miss but he's 40 years of age and you do get slower. Hopefully he is."

Costello admits he needs to leave the Crumlin Gym swiftly as Sutcliffe's case for McGregor draws one in. McGregor is now a shorter price with bookmakers to beat Mayweather than New Zealand's world heavyweight champion Joseph Parker is to overcome Anthony Joshua, should they ever meet.

Mayweather has been inactive, yes. But he has looked visibly leaner for months and vowed to train behind closed doors this time, staying away from the hive of cameras which notoriously film his sweat-heavy workouts.

Away from the nostalgia and atmosphere of the Crumlin Gym, Costello adds: "I have seen Mayweather on the punch bag with dozens of camera crews around him. He was throwing every punch like his life depended on it. Nothing cosmetic. It's that remarkable dedication.

"He has a 20-year hard-won reputation to defend and that's why I think he will be more than ready."

McGregor lost to Nate Diaz at UFC 196 before winning the rematch five months later

There are theories a shock can be built around. McGregor brings the tricky southpaw style Mayweather has seen less of. McGregor is rough and unpredictable, perhaps akin to Marcos Maidana, who worked Mayweather hard enough to earn a rematch in 2014. McGregor is 12 years younger and active in contrast to a man who retired almost two years ago.

Yet Bunce sees few obstacles: "When you have fought at the level Mayweather has, when you have made the foot adjustments he has made when your timing goes a little bit, which he says he has had to do. That man cannot lose to an absolute raw novice, it cannot happen.

"Think of the trainers who have sat there and plotted to beat Mayweather. Some fighters had amazing world class trainers yet not one of them left with a result. Mayweather can be horrible to watch fight but he is always 100% prepared."

Picking the boxer lends a common sense to a bout which seems to defy the very concept. For the masses, it is the only conceivable outcome. But then, it only takes one punch.

"Whatever happens, we are proud of him anyway," says Sutcliffe. "Please God, he's in with a puncher's chance."